Express this number in scientific notation. $0.000\;402$
Count the zeroes to the right of the decimal point before the leading $\leadingColor{4}$ : there are $3$ zeroes If you count the leading digit $\leadingColor{4}$ and those zeroes , there are $\exponentColor{4}$ digits to the right of the decimal point. So: $0.000\;402 = \leadingColor{4}.02 \times 10^{\exponentColor{-4}}$